Due to the ever escalating price of petroleum and the increasing competition between foods and other biofuel sources, there is a greater interest in algaculture (farming algae) for making biofuels such as biodiesel, bioethanol, biogasoline, biomethanol, and biobutanol. One proposed benefit from the production of biofuels from algae lies in helping to stabilize the concentration of carbon dioxide in the atmosphere at its present level because during photosynthesis, algae and other photosynthetic organisms capture carbon dioxide and sunlight and convert those into oxygen and biomass.
As those skilled in the art are aware, there are two basic processes used to grow microbes such as algae and/or bacteria, in large amounts e.g. for the biodiesel generation. One process is to use open ponds and the other is to use closed reactors.
The open pond process has the advantages of being easy to build and operate; having low energy costs to operate; providing for easy cleaning of the reactor; and the microbes use CO2 from the environment. However, the open pond method has certain disadvantages including that genetically engineered microbes may not be used due to governmental regulations; water evaporates and thus must be replenished; the microbe culture is susceptible to contamination by other microbes that will result in lower yields; UV light from the sun kills microbes; it is difficult to control the temperature; and artificially feeding microbes with CO2 for higher yields is difficult.
Closed bioreactors have the advantages that genetically engineered microbes that give higher yields cannot escape into the environment, the water in the system does not evaporate, lack of contamination by other microbes, UV light from the sun that kills microbes can be filtered out by the reactor walls, temperature control, although still difficult, can be manageable; and CO, from power plants, breweries, etc. can be artificially fed to increase yield.
Closed bioreactors too have disadvantages, such as being expensive to build; having higher energy costs to operate; bag reactors need less energy than pipe reactors that require the microbe solution to be pumped through the pipes; pipe reactors with high diameters need high turbulent flow to expose all algae to sunlight which results in high energy needs; pipe reactors with high diameters need high wall thicknesses which lowers the light transmission; and CO2 needs to be artificially fed.
Various artisans have attempted to address the deficiencies of bioreactors with differing degrees of success.
Sears, in US Published Patent Application No. 2007/0048859, describes an apparatus and system made of closed bioreactors for aquaculture and harvesting. In certain embodiments, the system of Sears is said to contain bags with various layers, including a thermal barrier layer, which may be used to contain the aquaculture and/or to thermally regulate the temperature of the aquaculture. The system may include various mechanisms for moving fluid within the system, such as a roller type mechanism, and may provide temperature regulation by compartmentalization of the fluid to regulate absorption of solar radiation and/or conductive or emissive heat loss and gain. Sears states that various mechanisms may be used to harvest aquatic organisms grown in the apparatus and process them into commercially useful products, such as biodiesel, methane, animal or human food, substrates for polymer synthesis or other chemical products.
US Published Patent Application No. 2007/0092962 in the name of Sheppard describes a device and method for carbon dioxide sequestering involving the use of a photo-bioreactor with light emitting diodes (“LED's”) for the cost-effective photo-fixation of carbon dioxide (CO2). This device and method of Sheppard is said to be useful for removing undesirable carbon dioxide from waste streams.
Kertz, in US Published Patent Application No. 2007/0289206 describes a method and apparatus for sequestering CO2 using algae. The device made of a plurality of vertically suspended bioreactors, each bioreactor being translucent and including a flow channel formed by a plurality of baffles. A culture tank containing a suspension of water and at least one algae and including a plurality of gas jets for introducing a CO2 containing gas into the suspension. The culture tank is in fluid communication with an inlet in each channel for flowing the suspension through the channel in the presence of light. A pump pumps the suspension into the channel inlet.
Woods et al., in US Published Patent Application No. 2008/0153080, detail a device for growing genetically enhanced aquatic photoautotrophic organisms in a stable culture, causing the organisms to produce ethanol, and then separating, collecting, and removing the ethanol in situ.
US Published Patent Application No. 2008/0160591 in the name of Wilson et al., describes a scalable photobioreactor system for production of photosynthetic microorganisms such as microalgae and cyanobacteria. In various embodiments, this system may include the use of extended surface area to reduce light intensity and increase photosynthetic efficiency, an external water basin to provide structure and thermal regulation at low cost, flexible plastic or composite panels that are joined together make triangular or other shapes in cross-section when partially submerged in water, use of positive gas buoyancy and pressure to maintain the structural integrity of the photobioreactor chambers and use of structure to optimize distribution of diffuse light. Other embodiments of Willson et al., concern air tubes comprised of plastic film at the bottom of each photobioreactor chamber to provide sparging air bubbles to the chamber. The photobioreactor system design also contains gas exchange, temperature control, air pumping, liquid pumping, filtration, media recycling and harvesting methods. For biofuels production, the photobioreactor system is said to include a separate growth photobioreactor and secondary stress reactor.
Hazelbeck et al., in US Published Patent Application No. 2009/0081743, provide a portable system and method for producing biofuel from algae. In the portable system, a chemostat and a plug flow reactor formed from plastic bladders are interconnected. Further, an algae separator is in fluid communication with the plug flow reactor for removing algae cells. Also, the system of Hazelbeck et al., includes a device for processing biofuel from the algae cells. The system includes a temperature controller to maintain desired temperatures in the chemostat and plug flow reactor for algae growth and intracellular algae production. To further support algae cell growth, the system includes a device for capturing carbon dioxide and delivering the carbon dioxide to the chemostat.
WO2007/098150 in the name of Hu et al. provides photobioreactors, modules thereof, and methods for use in culturing and harvesting algae and cyanobacteria. The photobioreactors of Hu et al. are constructed of a container adapted for holding fluid, which is made of opposing first and second sidewalls, wherein at least one of the first and second sidewalls is transparent; opposing first and second endwalls; a container bottom; and a container cover, wherein the first and second sidewalls has a plurality of separate sections, and wherein the separate sections are in fluid communication; support struts for connecting the plurality of separate sections of the first and second sidewalls; at least one inlet port in fluid communication with the container; at least one outlet port in fluid communication with the container; an aeration system in fluid communication with the container; and a temperature control system connected to the container so as to control temperature of fluid within the container.
Vermaas et al. in WO2008/051865 disclose a system and method for growing photosynthetic cells in conduit. The system and method supply light, CO2 and nutrients to the cells. The system and method also dampen thermal variations in the conduit. The system of Vermaas et al. contains: at least one conduit having an outer surface, an inner surface, an inner volume, a length, and at least a portion that permits sunlight to pass into the inner volume during use, wherein at least a portion of the at least one conduit is exposed to sunlight during day; a thermal dampening system in operable relationship to the at least one conduit; a CO2 supply system configured to supply CO2 to the inner volume during use; a nutrient-supply system configured to supply nutrients to the inner volume during use; and a separation system configured to remove the photosynthetic cells from the at least one conduit during use.
WO2009/051478 in the name of Van De Ven et al., describes a photobioreactor for the production of phototropic organisms, especially (micro)algae. The reactor is made of at least a reactor component in which a mixture of a liquid and some phototropic organisms has been or is to be introduced, where the reactor component has one or more tubes whose walls are at least partly transparent in order to allow daylight to enter the reactor component to enable the organisms in it to carry out their photosynthesis, also having an inlet, connected to the reactor component, for introducing the liquid and/or the phototropic organisms, an outlet, connected to the reactor component, for removing the mixture of the liquid and the resulting phototropic organisms, as well as a cleaning system connected to the reactor component, for the mechanical cleaning of the inside surface of the tubes so that it can continue to allow sufficient daylight to enter for the photosynthesis. The cleaning system of Van De Ven et al. has a first cleaning station, which is mounted between the inlet and the reactor component, a second cleaning station, which is mounted between the reactor component and the outlet, a cleaning tool that can move to and fro between the cleaning stations, along the reactor component with the shape and size of the cleaning tool being adjusted according to the inside surface of the walls of the tubes of the reactor component in order to clean these walls by the movement of the cleaning tool.
Van De Ven et al., in WO2009/051479 detail a photobioreactor for the production of phototropic organisms, especially (micro)algae, where the reactor is constructed of at least a reactor component into which a mixture of a liquid and phototropic organisms has been or is to be introduced, with the reactor component having a reactor vessel and one or more tubes connected to the reactor vessel. The reactor vessel is essentially protected from daylight, and the tubes are at least partly transparent, so that daylight can penetrate the reactor component to enable the organisms to carry out their photosynthesis. One or more floats ensure buoyancy for at least the tubes of the reactor component when the bioreactor is placed in an expanse of water, especially a lake or the sea. Van De Ven et al. also provide a method for the production of phototropic organisms, especially (micro)algae, involving the provision of a photobioreactor; the introduction of a mixture of a liquid and phototropic organisms into the photobioreactor; the placement and floating of at least the transparent tubes of the bioreactor in an expanse of water, especially a lake or the sea; and growing the microorganisms under the influence of daylight entering the transparent tubes.
Thus, there continues to exist a need in the art for photobioreactors for algae growth (e.g. for biofuel generation) that are less expensive to set up and to operate than conventional pipe reactors and which give high algae yields.